A Biological Safety Cabinet (BSC) is a specific engineering control used in the biological laboratory to prevent exposure to or the contamination of biohazardous agents. BSCs should be used whenever there is a risk of splash or aerosol formation of biohazardous or potentially biohazardous materials. BSCs work by manipulating air flow surrounding the area where work is being done such that the majority of biohazardous aerosols generated inside the BSC remain in containment while the majority extraneous laboratory aerosols remain outside of containment.
BSCs are divided into three classes (I, II, III) with class II being subdivided into five types (A1, A2, B1, B2, C1). The type of cabinet to be used will depend on the Biosafety Level of the microorganism as specified by CDC-NIH guidelines. For Biosafety Level 1 (BSL-1) microorganisms, standard microbiological practices will provide adequate protection. However, if additional protection is desired, any class of cabinet may be used by personnel working with these microorganisms. Class I and II Biosafety Cabinets will be used for low to moderate hazard microorganisms of Biosafety Levels 2 and 3. The main difference between the two is that Class II cabinets provide protection to personnel and the microorganism and Class I cabinets only provide protection to personnel. The most commonly used BSC is the Class II Type A1 or A2 cabinet, a figure of which can be found below.
Class III Biosafety Cabinets (also known as Glove Boxes) are required when working with high hazard microorganisms at Biosafety Level 4 (BSL-4). These cabinets are totally enclosed to provide the highest possible protection to personnel and the microorganisms. It is also important to note that glove boxes are also required for experiments using radioactive solids that may become airborne or with other highly toxic chemicals. Regardless of the type of research being conducted, it is important to follow safe practices and guidelines in order to minimize possible exposure.
When working with BSCs please abide by the following guidelines:
- All individuals working with a BSC must be trained in the proper operation, disinfection, and safe practices before starting work.
- Ensure BSC is within certification date, this can be found on the certification sticker located on the front of the BSC. If BSC is not within certification date please notify the Office of Environmental Safety and Health. Never use a BSC that is not certified.
- Never store items on top of the biological safety cabinet.
- Never store items inside the BSC that impede or otherwise disrupt the airflow. BSCs may not be used for storage of materials when not in use.
- Always wear proper PPE as determined by a risk assessment such as a gown, face/eye protection, a surgical mask, and a double set of gloves when working in a BSC.
- Never put your head inside the BSC, utilize mechanical devices to reach far areas.
- The BSC should be turned on at all times when working inside or when biohazardous agents are inside.
- The UV light should be turned off when working in the BSC as it can cause skin or eye damage.
- Always clean the BSC and other equipment before and after use. Note that a UV light, if present, does not provide adequate disinfection. All BSC disinfection procedures require the use of a facility approved disinfectant as determined by the risk assessment.
- Always disinfect items (including gloved hands) before placing into or removing from the BSC. This applies even when items are within proper containment such as a leak proof container or other facility approved containment.
- Place all disinfected items required for the experiment, including biological waste containers within the biological safety cabinet before starting the experiment in order to minimize the movement of hands.
- Utilize aseptic technique at all times.
- Move arms using straight in and straight out movements, as opposed to sweeping arms in a sideways motion which displaces more airflow, creating turbulence.
- Flames in the cabinet can damage the HEPA filter, use flame with pilot light for momentary activation if absolutely necessary or use a micro-incinerator.
- Collect waste/sharps within the cabinet using facility approved containers.
- If a spill occurs within the BSC, keep the unit running and immediately implement spill clean up procedures.
- A BSC does not provide the same level of chemical protection (if any) as Chemical Fume Hoods (CHF) when working with volatile chemicals.
- Laminar flow hoods and clean benches do not provide the same level of protection as biosafety cabinets. Under no circumstances may hazardous chemicals or biohazardous material be used in a laminar flow hood. All laminar flow hoods and clean benches should have a notification sign denoting their incompatibility with hazardous materials.
Biosafety Cabinets utilize high efficiency particulate air (HEPA) filters to capture biological agents and other particles. This filtered air is then recirculated within the BSC or exhausted. HEPA filters are efficient at capturing particles but are unable to capture volatile or toxic chemicals. The use of volatile or toxic chemicals inside a BSC can result in the recirculation or build up of that chemical inside the BSC unit or in the surrounding area. This could potentially create a flammable risk, impact research results, or lead to personnel exposure.
It is important to know what percentage of air is recirculated within your BSC unit as well as how much air is exhausted (if any).
- Class II A1 and A2 BSCs are designed to recirculate 70% of the HEPA filtered air within the BSC and exhaust 30% into the room or a duct.
- Class II B1 BSCs are designed to recirculate 50% of the HEPA filtered air within the BSC and exhaust the remainder into a duct.
- Class II B2 BSCs are designed to directly exhaust all air into a duct.
The major issues for using a chemical in a BSC relates to the chemical’s flammability and toxicity. A build up of flammable vapors within the BSC may cause a fire or explosion and the buildup of toxic vapors may result in personnel exposure or an impact to research results. The use of some nonvolatile chemicals such as aerosolized acids can damage the HEPA filter as well.
The Center For Disease Control’s Biosafety in Microbiological and Biomedical Laboratories 6th edition (BMBL) indicates that:
- “Small quantities of volatile toxic chemicals or radionuclides can be used in a Type A2 cabinet only if it exhausts to the outside via a properly functioning canopy with exhaust alarm.”
- “The Class II, Type B cabinet originated with the National Cancer Institute (NCI)-designed Type 212 (later called Type B) BSC (Figure 5a) and was designed for manipulations of small quantities of toxic volatile chemicals with in vitro biological systems.”
- “Class II, Type B2 BSC This BSC is a total-exhaust cabinet; no air is recirculated within it (Figure 6). This cabinet provides simultaneous primary biological and chemical (small quantity) containment”
- “Class II, Type C1 BSC This BSC is similar to a Type B1 BSC in that it has a special region of the work area intended for work with toxic volatile chemicals that are exhausted from the building”
If a hazardous chemical is to be used in a BSC, a thorough risk assessment must be conducted and the chemical quantity must be limited. It is best to utilize a chemical fume hood whenever possible when handling or preparing hazardous chemicals for application. If gaseous, vaporized, or aerosolized chemicals are generated in a BSC it is imperative to ensure that the quantity being generated will not cause a flammable or toxic risk.
More information on biosafety cabinets can be found utilizing the following resources